Not sure if I am seeing it correctly but one thing you might consider is that if the side of the rubbermaid tub (where there are no latches) is very close to the edge of the board above it, it may be possible for the snake to lift the lid by pushing the side of the tub outward.
If she was 35 inches long, she is longer than the tub is wide and I have seen mine brace their tail against one side of a tank and force their head along the other side. Their bodies will be in a strong S-shape and just quivering from the effort they are making.
I have one male that was determined to escape and he could put a lot of force into deforming the side of a tub. Once the side is pushed outward the seal at the top is flattened and not as secure. Corns can also really flatten out when they want to, amazing what they can get though. You might want to consider deeper shelves, especially for the longer tubs that are loose in the middle.
What is really suprising is that she made a break for it after having been housed in the tub for so long. Ours usually try for a month at most after going in a new enclosure and then give up and resign themselves.
Best of luck in finding her - she isn't gravid is she?